In the field of electronics, mounting technologies for bonding an electronic part with a substrate, and for bonding substrates together on which electronic circuits and electronic wirings are respectively provided are now advancing. Objects to be bonded by such mounting technologies include, on bonding surfaces, electrodes which are electrically connected to electronic circuits or the like. When the electrodes are connected together, electrical connection between the objects to be bonded is established.
There are always demands for downsizing and weight reduction with respect to electronic apparatuses. In accordance with such demands, high densification and refinement of circuit patterns for an electronic circuit, and the like, are advancing. Hence, a demand for improving the alignment precision between the objects to be bonded together is now increasing.
In order to meet such a demand, a bonding method of causing the objects to be bonded together to be in contact with each other, measuring the positional displacements of the respective objects, correcting the positional displacement and aligning both the objects, and then bonding the objects together is disclosed.
In the meantime, when the objects that are planar wafers are to be bonded together, the area of the bonding plane is large in comparison with, for example, a chip. Hence, when respective flat bonding surfaces of the planar wafers are caused to face with each other and bonded, air may be trapped in between the bonding surfaces, and thus voids may be produced. This results in a defective product.
Accordingly, a scheme of aligning wafers relative to each other, pressing the central portion of the wafer so as to be bowed toward the opposing wafer to be bonded together, and then bonding those wafers is applied. According to this scheme, with the outer circumferential portion of the wafer being held, the bonding surface of the wafer is deflected in such a way that the central portion is depressed and becomes convex toward the opposing wafer, thereby contacting the bowed portion to the opposing wafer. In this case, the bowed wafer has the convex central portion that comes in contact with the bonding surface of the opposing wafer. Subsequently, the bowed wafer is released. In this case, the bowed wafer recovers to the original planar shape, and is bonded with the opposing wafer across the entirety of the bonding surfaces.
In this case, while the bowed wafer is recovering to the original planar shape, since the bowed wafer contacts the opposing wafer in sequence from the convex central portion to the outer circumferential portion, air between the wafers is pushed out to the exterior, and thus trapped air between the respective bonding surfaces of the wafers is prevented.